How did the universe begin?

It took quite a bit more than seven days to create the universe as we know it today.Our universe was born about 13.7 billion years ago in a massive expansion that blew space up like a gigantic balloon,

By looking far out into space we are also looking far back into time, back toward the horizon of the universe, back toward the epoch of the Big Bang.” ― Carl Sagan, Cosmos

Before the Big Bang, there was no time or space. The Big Bang marked the beginning of the universe’s expansion from a singularity (or something close to a singularity) — a single point that was infinitely small, infinitely hot, and infinitely dense.

Scientists have also discovered a predicted thermal imprint of the Big Bang, the universe-pervading cosmic microwave background radiation. And we don’t see any objects obviously older than 13.7 billion years, suggesting that our universe came into being around that time.

“All of these things put the Big Bang on an extremely solid foundation,” said astrophysicist Alex Filippenko of the University of California, Berkeley. “The Big Bang is an enormously successful theory.”

Since the Big Bang, the universe has gone through several eras distinguished by the behavior of the universe’s fundamental forces and particle

Planck Era

Though physicists have a decent understanding of the early stages of the universe, the immediate fractions of a second following the Big Bang, known as the Planck Era, are not well understood. From the moment of initial expansion to 10-43 seconds afterwards, cosmologists suspect that the four fundamental forces at work in the universe today (strong, weak, electromagnetism, and gravity) were combined into a single unified force.

Grand Unification Era

The Grand Unification Era followed the Planck Era, taking place between 10-43 seconds and 10-35 seconds. The era began with gravity’s separation from the other three forces and ended with the separation of the strong force from the electroweak force.

Electroweak Era

At the beginning of the Electroweak Era (10-35 to 10-10 seconds), the strong force-decoupled from the electroweak force, releasing a tremendous amount of energy and triggering a sudden rapid expansion known as inflation. As space expanded more rapidly than the speed of light, extremely energetic interactions created elementary particles such as photons, gluons, and quarks. The era ended with the separation of electromagnetism from the weak force.

Elementary Particle Era

Between 10-10 seconds and 0.001 second, the Elementary Particle Era, a “particle soup” filled the universe. Quarks and antiquarks, electrons and positrons, and other particles and antiparticles continually swapped mass for energy via matter-antimatter collisions. As the universe cooled, the temperature dipped too low to re-create pairs of particles from photons and the particles continued to annihilate without being replaced. A slight asymmetry between the amount (or possibly the behavior) of matter and antimatter enabled matter to dominate and become the universe’s primary ingredient. The cooler temperature also enabled the strong nuclear force to draw quarks together to form protons and neutrons.

Era of Nucleosynthesis

Fusion continued in the Era of Nucleosynthesis (0.001 seconds – 3 minutes), when protons and neutrons combined into the first atomic nuclei, hydrogen, some of which fused further into helium and lithium. Cooling continued and soon temperatures dipped too low for fusion to continue in the Era of Nuclei (3 minutes – 380,000 years). Big Bang nucleosynthesis had left the universe with roughly 75% hydrogen nuclei, 25% helium nuclei, and trace amounts of lithium and deuterium nuclei. The plasma of positively charged nuclei and negatively charged free electrons filled the universe, trapping photons in its midst.

Era of Atoms

The Era of Atoms (380,000 years – 1 billion years or so) began as the universe finally cooled and expanded enough for the nuclei to capture free electrons, forming fully-fledged, neutral atoms. Previously trapped photons were finally free to move through space, and the universe became transparent for the first time. These photons have been passing through space ever since, forming thecosmic microwave background. The universe’s expansion has redshifted the initially energetic photons to microwave wavelengths. The CMB also marks the furthest point back in time we can observe — the time before is sometimes referred to as the dark age.

Big Bang Theory – Common Misconceptions

There are many misconceptions surrounding the Big Bang theory. For example, we tend to imagine a giant explosion. Experts however say that there was no explosion; there was (and continues to be) an expansion. Rather than imagining a balloon popping and releasing its contents, imagine a balloon expanding: an infinitesimally small balloon expanding to the size of our current universe.

Another misconception is that we tend to image the singularity as a little fireball appearing somewhere in space. According to the many experts however, space didn’t exist prior to the Big Bang. Back in the late ’60s and early ’70s, when men first walked upon the moon, “three British astrophysicists, Steven Hawking, George Ellis, and Roger Penrose turned their attention to the Theory of Relativity and its implications regarding our notions of time. In 1968 and 1970, they published papers in which they extended Einstein’s Theory of General Relativity to include measurements of time and space.According to their calculations, time and space had a finite beginning that corresponded to the origin of matter and energy.”The singularity didn’t appear in space; rather, space began inside of the singularity. Prior to the singularity, nothing existed, not space, time, matter, or energy – nothing. So where and in what did the singularity appear if not in space? We don’t know. We don’t know where it came from, why it’s here, or even where it is. All we really know is that we are inside of it and at one time it didn’t exist and neither did we.

Another idea

Most cosmologists regard inflation as the leading theory for explaining the universe’s characteristics — specifically, why it’s relatively flat and homogeneous, with roughly the same amount of stuff spread out equally in all directions.

Various lines of evidence point toward inflation being a reality, said theoretical physicist Andy Albrecht of the University of California, Davis. “They all hang together pretty nicely with the inflationary picture,” said Albrecht, one of the architects of inflation theory. “Inflation has done incredibly well.”

However, inflation is not the only idea out there that tries to explain the universe’s structure. Theorists have come up with another one, called the cyclic model, which is based on an earlier concept called the ekpyrotic universe.

This idea holds that our universe didn’t emerge from a single point, or anything like it. Rather, it “bounced” into expansion — at a much more sedate pace than the inflation theory predicts — from a pre-existing universe that had been contracting. If this theory is correct, our universe has likely undergone an endless succession of “bangs” and “crunches.”

“The beginning of our universe would have been nice and finite,” said Burt Ovrut of the University of Pennsylvania, one of the originators of ekpyrotic theory.

The cyclic model posits that our universe consists of 11 dimensions, only four of which we can observe (three of space and one of time). Our four-dimensional part of the universe is called a brane (short for membrane).

There could be other branes lurking out there in 11-dimensional space, the idea goes. A collision between two branes could have jolted the universe from contraction to expansion, spurring the Big Bang we see evidence of today.

“If the fate of the universe was decided in a single moment at the instant of the Big Bang , that was the most creative moment of all.”
― Deepak Chopra